1. Field of the Invention
The present invention is directed generally to an apparatus for verifying the correct position of a temporary transvenous cardiac pacing lead in the ventricular cavity of a heart prior to emergency pacing, and more particularly to a system allowing visual inspection of pacing lead position by direct electrical connection between the temporary pacing lead and a conventional ICU physiological monitor. It may also be used to facilitate random intracardiac recordings of rhythm.
2. Description of The Related Art
Medical instrumentation for the care and monitoring of the critically ill cardiac patient has improved significantly over the last decade, due in part to improved design and operability of temporary cardiac pacing leads and cardiac monitors such as the conventional electrocardiograph (ECG). Continuous monitoring of a cardiac patient's condition allows a physician to take immediate corrective action in the event of a highly irregular heartbeat or a heart attack.
When a cardiac patient suffers an arrythmia of the type requiring intervention of an internal pacing system, a physician will typically insert a temporary pacing lead into the heart cavity which functions to exogenously stimulate the myocardium, increasing a dangerously slow rhythm or overriding and controlling a dangerously fast one. The temporary pacing lead is generally inserted into the heart chamber percutaneously with either fluoroscopic or electrocardiographic guidance. The pacing lead is directed along a path through the superior vena cava or inferior vena cava, right atrium, across the tricuspid valve and into the right ventricle where it is positioned abutting the ventricular wall. The close proximity of the pacing electrode to the ventricular wall is mandatory as any increase of this distance poses a risk of failure of the electrode to capture the heart muscle (myocardium) and hence reoccurrence of the patient's initial arrhythmia.
In order to correctly position the pacing lead against the ventricular wall, the lead is configured as a sensing electrode which is connected to the voltage lead of an electrocardiograph so that the characteristic electrical signals representing the complex electrical operation of the heart may be examined by the attending physician. By assessing the relative sizes and shapes of the P-wave and QRS complex signals, the physician is able to accurately determine the position of the pacing lead within the heart. Once the pacing lead is correctly positioned, heart pacing by means of an external power source may begin.
However, an electrocardiograph is a costly, complex, and highly specific piece of medical equipment which must be operated by a skilled technician. Consequently, undue delay may be incurred in responding to a cardiac emergency because either an electrocardiograph or a technician is unavailable at the time of the emergency.
In many hospitals, intensive care (ICU) and/or cardiac care (CCU) facilities have been designated for the care of critical or cardiac patients. These facilities are equipped with devices adapted to monitor the patient's vital signs (e.g., heart rate, respiratory rate, blood pressure, etc.) and provide a telemetric link between each patient and a multi-purpose physiological monitoring unit termed an ICU monitor. Vital sign data is derived through spaced apart skin contact electrodes, disposed about the body, which sense the minute voltage changes accompanying physiological activity. The sensed voltage changes are amplified and displayed on an oscilloscope type screen for easy visual inspection. ICU monitors are generally available. However, the nature of the electrical connectors of the pacing lead and the ICU monitor sensing leads differ substantially from each other.
Pacing lead connectors are elongated rigid conductors adapted for bayonet-type insertion into the mating plug of a cardiac stimulation battery, and in some cases the voltage sensing lead of an electrocardiograph machine. In contrast, ICU monitors typically employ a five-way standard lead configuration with unipolar electrodes. One of the electrodes is attached adjacent the lower right ribcage of the patient as a signal reference, while monitor signals are developed as potential differences between associated pairs of additional electrodes. The electrodes themselves are generally circular, and contact the body at a concave surface through a silver compound applied to the skin. Electrical connection to the ICU monitor is made by a flanged snap fit connector which engages a mating member extending outward from the electrode's upper surface.
In addition, many ICU monitors are configured for receiving a voltage input, which requires that signals induced into the sensing leads be dropped across an associated impedance. Since the electrical signals transmitted by a pacing lead to an external device are invariably current signals, pacing lead impedances are strictly limited. In most cases, the impedance values of the entire lead may not exceed 30 ohms. Consequently, the nature of the electrical signals provided by a pacing lead and those required by an ICU monitor may be substantially incompatible as well.
It is known to utilize an alligator clip in an attempt to electrically couple the appropriate sensing lead of the monitor with an oscilloscope. However, this is typically not a stable connection, and the alligator clip may not have the correct electrical characteristics to enable the oscilloscope to properly display accurate signals from the myocardium. In addition, the pacing lead has a proximal terminal which is exposed and this presents a potential danger to the patient.